The use of cellular communication systems having mobile devices which communicate with a hardwired network, such as a local area network (LAN) or a wide area network (WAN), has become widespread. Retail stores and warehouse, for example, may user cellular communications systems with mobile data terminals to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects. Such systems are also utilized for cellular telephone communications to allow users with wireless telephones to roam across large geographical regions while retaining telephonic access. Paging networks also may utilize cellular communications systems which enable a user carrying a pocket sized pager to be paged anywhere within a geographic region.
A typical cellular communications system includes a number of fixed access points (also known as base stations) interconnected by a cable medium often referred to as a system backbone. Also included in many cellular communications systems are intermediate access points which are not directly connected to the system backbone but otherwise perform many of the same functions as the fixed access points. Intermediate access points, often referred to as wireless access points or base stations, increase the area within which access points connected to the system backbone can communicate with mobile devices.
Associated with each access point is a geographic cell. The cell is a geographic area in which an access point has sufficient signal strength to transmit data and receive data from a mobile device such as a data terminal or telephone with an acceptable error rate. Typically, access points will be positioned along the backbones such that the combined cell area coverage from each access point provides full coverage of a building or site.
Mobile devices such as telephones, pagers, personal digital assistants (PDA's), data terminals etc. are designed to be carried throughout the system from cell to cell. Each mobile device is capable of communicating with the system backbone via wireless communication between the mobile device and an access point to which the mobile device is registered. As the mobile device roams from one cell to another, the mobile device will typically deregister with the access point of the previous cell and register with the access point associated with the new cell. In order to provide sufficient cell area coverage, access points (or the antennas associated with each access point) within the cellular communications system typically are distributed at separate physical locations throughout an entire building or set of buildings.
Recently a standard for wireless local area networks (WLANs) known as the IEEE 802.11 standard has been adopted and has gained acceptance among the industrial, scientific and medical communities. The IEEE 802.11 standard for WLANs is a standard for systems that operate in the 2,400-2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The IEEE 802.11 RF transmissions use multiple signaling schemes (modulations) at different data rates to deliver a single data packet between wireless systems. The latest IEEE 802.11 wireless LAN uses a band of frequencies near 2.4 Ghz for direct sequence spread spectrum transmissions. Another recently adopted short-range standard has evolved known as the Bluetooth standard (see www.bluetooth.com). The Bluetooth standard is a low-cost short range wireless connection which uses much of the same range of frequencies for its frequency-hopping spread spectrum transmissions as the IEEE 802.11 standard. In some applications, it is appropriate to use systems employing IEEE 802.11 concurrently with other systems using the Bluetooth standard. Consequently, there is expected to be considerable interference between the two systems. Early theoretical studies show widespread use of Bluetooth standard reducing the band-width of a co-located 802.11 LAN by as much as 20-50%. It is also possible for 802.11 transmissions to interfere with Bluetooth.
Schemes proposed for mitigating the interference of 802.11 and Bluetooth generally involve adding intelligence to the networks so that they will sense each other and avoid collisions as much as possible. This is workable but complicated. Such methods will slow initial deployment of IEEE 802.11 and Bluetooth together, and add to the cost of maintenance.
Accordingly, there is a strong need in the art for a system and method that overcomes the aforementioned problems.